1. Field of the Information
The present invention relates to an inkjet image forming apparatus and inkjet image forming method.
2. Discussion of the Background
Inkjet recording technique is a technique, and the technique made a ink to liquid spot by using a pressure ondemand form and a charge control form, and adheres the ink on a recording medium such as paper according to a image information.
The inkjet recording technique is preferably used in image forming apparatus such as printers, facsimiles, and copiers.
The inkjet recording technology can record ink to a recording medium using a simpler apparatus, as compared to indirect recording techniques, such as electrophotography using a photoconductor, because the inkjet recording process can adhere the ink to the recording medium directly, and is expected to increase in use in the future.
Inkjet recording is a process using a low noise printer system, and discharging ink on a recording medium, such as paper, cloth, or plastic sheet. The main use is for directly printing letters and images. Further, inkjet recording does not need a printing master, and can efficiently print even one or a few prints, so is excepted from industrial use.
However, industrial recording has to form images on various kinds of recording media, but direct discharge types of recording cannot satisfy the requirements. Accordingly, inkjet recording by direct discharge is an image forming method that has significant restrictions in the type of image medium that can be used.
One of the concrete restrictions is the ability of the recording medium to absorb ink. Most ink components are liquid, so differences in absorption permeability of the ink can have an influence on image reproducibility. In particular, while using a recording medium that does not absorb liquid ink, adjacent ink spots often are found to mix, resulting in a phenomenon where the first formed ink spots can be drawn to mix with later formed ink spots. Therefore, image recording is very difficult, and permeation drying can't be used, making high speed printing very difficult. An alternative to printing methods using recording media that do not absorb ink is a method using an ink containing an ultraviolet curing resin, which is cured by ultraviolet irradiation.
For example, JP2004-42548 describes a method using ultraviolet curing type ink, and matches the application of ultraviolet irradiation with the timing of the discharge of a dot of ultraviolet curing type color ink to the recording medium, causing a rise in viscosity by pre-curing to a level such that neighboring dots are not mixed with each other, and then further irradiating with ultraviolet irradiation to complete curing.
JP2004-42525 describes a technology to improve the visibility of colored ink, reduce bleeding, and reduce the difference between images on various recording media. The method uses a radiation curing type white ink that is coated homogeneously as an under layer. The ink is then cured, to increase viscosity, by irradiation, and inkjet recording is carried out using the radiation curing type color ink set.
However, while the method of JP2004-42548 is reported to control bleeding, there remains the problem of differences between recorded images on various recording media, insufficient homogeneity and color unevenness, and the like, of line width cause by mixing between liquid particles. Further, the method of JP2004-42525 also provides insufficient homogeneity and color unevenness, and the like, of line width caused by mixing between liquid particles.
One possible solution that has been proposed is as follows; an ultraviolet radiation curing type clear liquid is coated on the recording medium as an under layer, and colored ink is discharged, to prevent bleeding and mixing between liquid particles. For example, JP2008-105382 is one such proposal. JP2008-105382 describes a method that can form high quality images. However, according to the invention of JP2008-105382, the invention prevents too much extending of ink particles, but it is difficult to achieve conditions sufficient for pre-curing. This results in unevenness, due to the presence of incompletely cured and nearly uncured particles, and the unevenness makes deference of extending of each particles.
To avoid the problem, a technology is considered that discharges ink to an uncured layer, then discharged ink penetrates the surface of the uncured under layer, but the ink particles are not confined by influence of the under layer and bleeding occurs due to the ink particles spreading slowly. However, ink spreading is dependent on time. If there is a time gap between discharge and curing of the particles, there is a problem that the time gap creates a gap of ink particle size.
The present invention aims to solve the above-mentioned problems.